The present invention relates to a permanent magnet positioning and retaining device and in particular relates to a direct current brushless motor, capable of keeping permanent magnets of rotor in place under high-speed revolution.
Conventional direct current brushless rotor comprises a rotor iron core, several arc-shaped permanent magnets around said rotor iron core, and a sleeve fit around and over said arc-shaped permanent magnets. Under revolution, the permanent magnets are pulled away in radial direction by centrifugal force so as to lose contact with the rotor iron core, thus creating magnetic impedance and affecting motor performance.
FIG. 1 shows a structural perspective of a sleeved direct current brushless rotor. In order to prevent magnetic flux leakage, gaps 15 and cut-off areas 14 are provided between adjacent arc-shaped permanent magnets 12. Under revolution, said gaps 15, however, prevent permanent magnets 12 from remaining in the same position and orientation. This causes instability in torque output and motor efficiency, produces noise and vibration, and affects overall motor performance.
FIG. 2 shows a structural perspective of a magnet positioning and retaining device in accordance with prior art U.S. Pat. No. 5,176,461. Though protrusions 24 provided between two permanent magnets 22 are intended for stopping the permanent magnets 22 from moving in circumferential direction, they are incapable of preventing said magnets 22 from shifting in radial direction. Furthermore, the centrifugal force generated by rotation forces the magnets 22 against the sleeve, causing stress, reducing and motor reliability and lifespan.
U.S. Pat. Nos. 5,828,152 and 6,084,330 are related prior arts with similar disadvantages shared by the embodiment of FIG. 2.
FIG. 3 shows a structural perspective of a magnet positioning and retaining device in accordance with the improved prior art U.S. Pat. No. 4,954,736. In the figure, the expanded portion 34 of an integral holding projection provided between two permanent magnets 32 fills the gap between two adjacent permanent magnets 32 so as to stop the movement of permanent magnets 32 in the circumferential direction. In addition, the near triangle-shaped structure provided on both ends of the contact region between a sleeve 33 and said expanded portion 34 can prevent radial shifting of permanent magnets 32. However, the good intention of reducing magnetic flux leakage by the cut-off design of permanent magnets 32 is offset by the use of integrally stamped silicon steel for said expanded portion 34, being a magnetic conducting material in direct contact with the magnets 32. Moreover, high cost associated with excess scrap material as a result of stamping process hinders said prior art from becoming commercially competitive.
Another related prior art U.S. Pat. No. 4,910,861 reveals plastic filling for the gap between permanent magnets. Yet in high-speed revolution, the loaded rotor generates heat, which softens plastic fillings and undercut their strength of holding permanent magnets in place. Again, the lifespan and reliability of rotor remain unsatisfactory.
The prior arts and the improved ones as discussed above fail to provide answers for resolving the aforementioned discrepancies. The quest to solutions stays a priority for those skilled in the art.
An object of the present invention is to provide a permanent magnet rotor magnet positioning and retaining device, capable of preventing circumferential and radial shifting of permanent magnets, thereby ensuring overall motor performance, reliability and lifespan.
Another object of the present invention is to provide a divider made from poor or non-magnetically conducting material for making direct contact with permanent magnets and for preventing magnetic flux leakage.
To that end, the present invention reveals a permanent magnet rotor magnet positioning and retaining device, comprising a sleeve, a rotor iron core, at least one arc-shaped permanent magnet, and a plurality of dividers wherein said sleeve has a hollow tubular structure; said rotor iron core comprises a least one groove circumferentially provided in the proper locations inside said sleeve; said arc-shaped permanent magnets of alternating poles provided between said sleeve and said rotor iron core are separated from one another by said dividers, said arc-shaped permanent magnets each having a cut-off area in outer perimeter corners of two adjacent permanent magnets so as to form a near triangle-shaped region between two adjacent permanent magnets; a plurality of dividers, provided between permanent magnets of alternating poles, comprises a base, a trunk and a rim; wherein said base is engaged with a groove so that the dividers are secured to the rotor iron core; said trunk fills the gap between two adjacent permanent magnets to prevent said permanent magnets from moving in circumferential direction; and said rim has a near triangle-shaped structure in close contact with said cut-off area (in outer perimeter corners of two adjacent permanent magnets) so as to prevent permanent magnets from moving in radial direction.
The following Description and Designation of Drawings are provided in order to help understand the features and content of the present invention.